Machinable stainless casting



patented @ec. W, t fit UNETEE STATES MACHINABLE STAINLESS CASTING FrankA. Fahrenwald, Chicago, Ill.

No Drawing. Application June 26, 1933, Serial No. 677,761

r 1 Claim. (Cl. 75-11) This invention relates to machinable stainless orrustless alloy-castings or articles, for example, pipes and tubes,together with valves, fittings, faucets and the like used in connectionthere- 5 with; also household utensils, such as kettles or pansdecorative objects such as plaques, nameplates and the like; and variousornamental forms requiring a surface stable under atmosphericconditions.

This alloy has proved particularly adaptable to the manufacture of partsfor centrifugal and reciprocating pumps, and for fittings and valvessuch as are employed in. the handling of corrosive liquids in variousindustries. Materials heretofore available for such purposes have beencast iron, bronze, various forms of plated ware, and, more latterly,some of the so-called stainless alloys containing, for instance, 18% ofchromium and 8% of nickel. I

A great demand has existed for a nickel-chromium or high chromium typeof casting for the above-named and similar uses, but due to the verygreat difflculty encountered in production, alloys of compositions knownheretofore have not been commercially available for these applications.The prime requisites for such an alloy, in

addition to surface stability, are ease of casting in the foundry andease of machining or otherwise working, to adapt the casting for somespecific use.

It has heretofore been claimed that for a casting to have corrosionresistingqualities and to be easily machinable, its carbon content mustbe low, and this is reiteratedthroughout the prior art. In my ownexperiments, undertaken to produce castings of these types, I haveemployed higher percentages of chromium and higher per centages ofcarbon and whereas I found at first, in common with the claims of theprior art, that when the chromium content or carbon content is increasedto only a medium degree'above the low carbon ranges constantlyheretofore specified, very great hardness, fragility and unmachina- 45bility resulted, yet if the chromium and carbon are increased far abovethat previously employed, the alloys again reach a machinable range incomposition and besides take on production characteristics which renderthem producible in forms hitherto consideredutterly impossible.

Whereas the older forms of stainless alloys are tough and'diflicult tomachine, my new alloy can be cut, drilled or filed with extreme caseand,

\ while it lacks the ductility or toughness of the low carbon alloys, Ihave been enabled to render it sufllciently strong and tough for all ofthe purposes hereinbefore enumerated.

All low carbon nickel-chromium alloys have a high shrinkage from liquidto solid and have a long range between solidness and liquidness dur- 5ing solidification, with resulting proneness to develop cracks andshrink holes during casting.

The older low carbon alloys are of high melting point, requiringexpensive refractory molding sands; whereas, my new alloy is of muchlower melting point and castings can be made in cheap sands ordinarilyemployed for gray iron castings. Likewise, regarding the requirement fora low carbon content and for stainless qualities in the older types ofalloys, I have found that high carbon percentages may be employedproviding the chromium content is increased proportionately. The basisof my new alloy casting: is a combination of iron, chromium andcarbonthe chromium varying between 30 and and the carbon between 1.25and 2.75%, to which, for reasons hereinafter described, I make nickeladditions varying from of 1% to 15%; one typical formula within theselimits being chromium 35%; nickel 2%; carbon 2%; and the balance iron,which has been found to answer well the conditions encountered incentrifugal pumps. Another formula, and one found resistant to 10%sulphuric acid, is chromium 34.9%; nickel 9% and carbon 1.9%. A straightchromium=iron casting containing 36.4% chromium and 2.20% carbon wasfound to possess the qualities of great fluidity in casting andmachinability when cast, but possessed the unfortunate characteristic ofgreat brittleness, besides lacking required resistance to corrosion. ButI have found that the brittleness is very rapidly eliminated by smalladditions of nickel; whereas, the resistance to corrosion isat the sametime thereby tremendously increased. Nickel-free castings of this 40type are so brittle as to render handling during production andmachining quite difficult, but the addition of even of 1% of nickelovercomes this deficiency; whereas 10% nickel renders the castings sotough that they can be readily straightened without heating to correctwar-pages introduced during a casting operation. Likewise, the highernickel alloys are progressively more immune to corrosion. But more than15% does not seem to improve the castings either physically orchemically to a degree sumcient to justify the greatly increased cost.

From my new alloy I have produced pans and hollow containers up to teninches in diameter of a wall thickness less than one-eighth of an inch.5

and long thin rails and the like up to six feet in length with onlyfive-sixteenths of an inch metal thickness.

Very intricate designs can be made from my alloy by the process ofcasting, and a very fine perfect surface can be produced. Incontradistinction to the previously known nickel-chromium alloys withlow carbon content which are very difficult to cast in many shapes orsections, I have found that this new high carbon, high chromium basealloy containing nickel can be cast into practically any shape or designpossible with brass or bronze. v

The new alloy is very .resistant to sulphuric acid, practically immuneto nitric and organic acids, and immune to the action of all of thecommoner alkaline solutions. It is completely immune against atmosphericcorrosion and will take a highly polished finish which retains itsluster equally as well as does the previously employed low carbon, lowchromium stainless alloy.

Castings made from this alloy can be manufactured from raw materialscosting less than one-half as much as castings of the low carbon type.Due to its lower melting point and.protection against oxidation, my newalloy can be melted in fuel fired furnaces at a cost reduced by 75% ascompared with electric furnaces. Foundry production costs are far lowerbecause of the cheaper sands permissible, higher yield, more perfectcastings and easy finishing or machining operations which, in thin aswell as thick sections, compare favorably with those of cast gray iron,in that they respond to ordinary finishing tools in the average machineshop manned with common skilled labor. V l

The formulas given are in terms of essential ingredients only.Percentages of molybdenum, tungsten, copper, manganese, etc. frequentlyencountered in iron or iron alloy castings may be present withoutdeparting from the spirit of the invention.

I claim:

A machinable stainless alloy casting consisting of iron, with chromiumabout 35%, nickel from of 1% to 15%, and carbon around 2%.

FRANK A. FAHRENWALD.

